1. The Field of the Invention
The present invention relates to means for mitigating the effects of unintentional impacts on solid propellant rocket motors. More particularly, the present invention relates to solid propellant rocket motors having material mitigants disposed within the rocket motor bore such that accidental explosion and ignition are avoided.
2. Technical Background
A major concern in the defense and aerospace industries is safety. Safety concerns continue to be at the forefront of the development of new products and devices for use in these, and other related industries. Safety concerns are very important when it is necessary to require people to work around devices which are potentially explosive, flammable, or which contain other types of energetic compositions, such as propellants and illuminants.
Problems in dealing with explosive, flammable, or energetic materials are heightened when such materials may potentially be used in combat situations, or during unconventional flight. In these situations, probabilities increase that the device will be impacted by a flying projectile or otherwise disturded. For example, in combat situations, it is not inconceivable that a stray projectile, such as a bullet, could penetrate a device containing an explosive or propellant material. When rocket motors are stored on ships or aircraft, the chance that they may fall or be bumped is increased. All of these situations present safety concerns because it is known that striking or disturbing these types of devices may lead to accidental ignition or explosiion.
Since modern combat operations depend heavily on the use of rocket motors to deliver ordinance, or to propel other types of devices, it is often necessary for combat personnel to operate in the presence of such rocket motors. This presents a direct safety risk in that there is also an increased chance of such motors being struck or unintentionally disturbed.
In response to these concerns, various government agencies and military services have issued "insensitive munitions" guidelines and related standards for materials used in the defense and aerospace fields. These guidelines and standards seek to assure that the chance of accidental ignition or explosion is minimized. Clearly these standards and guidelines, as well as safety concerns generally, present challenges in the manufacture of rocket motors and other similar types of devices.
It is well known that many rocket motors react violently when impacted with a bullet or high speed fragment. For example, the Standard Missile Motor is known to react explosively to bullet impact, as well as to fast and slow cookoff conditions. As a result, this rocket motor is not in compliance with the insensitive munitions requirements of the Department of Defense (known as DoD-STD-2105A), even though this device has wide application. Thus, while the Standard Missile Motor uses high performance components, it suffers from the drawback of not meeting insensitive munitions standards.
It will be appreciated that the typical rocket motor is comprised of several standard components. A rocket motor typically has an exterior case made of metal or filament wound composite materials. These materials are light weight, yet strong and resilient. Placed within the case is an insulation layer. This layer protects the case from the burning propellant, also contained within the case. In most modern rocket motors, a bore is disposed within the propellant grain. The typical bore is simply a cylindrical opening which runs through the length of the propellant grain. The bore may be specifically engineered to enhance the performance of the rocket motor. Thus, bores of various sizes, shapes, and configurations are found in the art.
It has been determined that one of the causes of violent reactions when rocket motors are penetrated by projectiles is the fragmenting of the propellant. Most propellants are comprised of energetic and oxidizing solids incorporated into a polymeric binder. Typically, rocket motor propellants have a high percentage of solids loaded in the binder. This results in propellants that are relatively frangible.
As a result, it is found that when a projectile penetrates a rocket motor and passes through the propellant grain, the propellant near the penetration tends to shatter and produce a cloud of propellant dust. As the projectile moves into the center of the propellant grain, and passes through the bore, shattered propellant is sprayed from one side of the propellant grain, through the bore, and onto the opposite side of the bore. It is found that when this shattered propellant cloud impacts with the far side of the bore, ignition or explosion may occur.
Thus, ignition of the fragmented, granular propellant is likely to occur during the expansion of the propellant cloud and during impact of the propellant cloud (and the projectile) with the far bore surface. Undamaged propellant in the bore may also be ignited from collision with the fragmented particles. Although burning fragments have been observed during the entrance and exit of the projectile, it appears that the main cause of rocket motor explosions is the interaction of the fragmented propellant with the rocket motor bore.
Accordingly, it would be a significant advancement in the art to provide rocket motors and similar devices which were safer to handle and use. In particular, it would be an advancement in the art to provide such devices which have the potential for meeting government insensitive munitions standards. In that regard, it would be an advancement in the art to provide means for controlling the flight and impact of fragmented propellant when a rocket motor is penetrated by a projectile in order to reduce the risk of ignition or explosion.
Such methods and apparatus are disclosed and claimed herein.